Graded index of refraction glass provides unique optical properties that are otherwise unavailable with conventional homogeneous glasses. For example, chromatic aberrations may be corrected within a single lens by a judicious selection of the profile of the index gradient, thereby reducing the number of components in an optical system by as much as a factor of two. Such GRIN glass is available from LightPath Technologies, Inc. (Albuquerque, N.Mex.) under the trademark GRADIUM.RTM..
The fabrication of such graded index of refraction glass has been disclosed in a number of references, including starting from powders, each having a different composition (U.S. Pat. No. 4,883,522, issued to James J. Hagerty et al), starting from stacked glass plates, each having a different composition (U.S. Pat. No. 4,929,065, issued to James J. Hagerty et al), and starting from glass frits, each having a different composition (U.S. Pat. No. 5,630,857, issued to Xiaojie Xu et al), all assigned to the same assignee as the present invention.
While each of these methods is certainly suitable for making GRIN glass lens blanks, the melting of powders or frit can lead to the formation of bubbles in the melt. The removal of bubbles requires processing time, thereby increasing production costs.
The problem of air bubble removal exists only in the case of preparation of GRIN glass from frit or powder. When large glass plates rather than frit are sintered, no bubbles will form, or will appear only in small amounts. However, this approach requires cutting and grinding these plates, and ensuring that each plate has the proper shape and weight. Fabrication of the plates entails undesirable expenditures of time.
Thus, a need exists for accelerating the process of bubble removal.